Mechanical air conditioning

Mechanical air conditioning relies on the laws of thermodynamics and heat transfer to cool indoor spaces. Unlike evaporative cooling (which adds moisture), mechanical AC removes heat and humidity using a refrigeration cycle. Below is a detailed breakdown of its core mechanical components and processes.

1. Core Mechanical Components

(1) Compressor

  • Function: Pressurizes refrigerant gas, raising its temperature.
  • Types:
    • Reciprocating (Piston-based, common in older systems).
    • Rotary (Compact, used in window/split ACs).
    • Scroll (Efficient, quieter, used in premium systems).
    • Screw/Centrifugal (For large commercial systems).

(2) Condenser Coil

  • Location: Outdoor unit.
  • Function: Releases heat from the refrigerant to the outside air.
  • Material: Typically copper or aluminum fins for better heat dissipation.

(3) Expansion Valve (or Metering Device)

  • Types:
    • Thermostatic Expansion Valve (TXV) – Precise refrigerant flow control.
    • Capillary Tube – Simple, fixed restriction (common in small ACs).
  • Function: Reduces refrigerant pressure, cooling it before it enters the evaporator.

(4) Evaporator Coil

  • Location: Indoor unit.
  • Function: Absorbs heat from indoor air as refrigerant evaporates.
  • Blower Fan: Circulates cooled air into the room.

(5) Refrigerant

  • Common Types:
    • R-410A (Replaced R-22, ozone-friendly).
    • R-32 (More efficient, lower global warming potential).
    • R-290 (Propane) – Eco-friendly but flammable.

2. The Refrigeration Cycle (Step-by-Step)

  1. Compression – Refrigerant (gas) is compressed, becoming high-pressure & high-temperature.
  2. Condensation – Hot gas flows through the condenser coil, releasing heat and turning into a liquid.
  3. Expansion – Liquid refrigerant passes through the expansion valve, dropping pressure & temperature.
  4. Evaporation – Cold refrigerant absorbs heat from indoor air, turning back into gas.
  5. Repeat – The cycle continues until the desired temperature is reached.